•A fluorescent resonance energy transfer (FRET) system was built for ratiometric sensing of Hg2+ using periodic mesoporous organosilica (PMO) nanoparticles as the scaffold.•Bis-silylated anthracene (Anth) and silylated Rhodamine 6G derivative containing spirolactam unit (R6G) were adopted as the energy donor and acceptor of FRET, which were arranged into the pore framework and channel, respectively.

A fluorescent resonance energy transfer (FRET) system was built for ratiometric sensing of Hg2+ in water with periodic mesoporous organosilica (PMO) nanoparticles (NPs) as the scaffold. The silylated rhodamine 6G with a spiro-ring (R6G) as the energy acceptor was covalently attached on the pore walls of anthracene (Anth) encapsulated PMO NPs, which played the role of energy donor. In the presence of Hg2+, the fluorescence emission from R6G in the pore channel was observed by exciting Anth in the framework, which means the emission energy of Anth can effectively funnel into R6G and excite it. The successful FRET from Anth to R6G should be attributed to the shortened distance between them attributed to the nanometer-sized pore system of PMO matrix, which finally leads to the emission of original colorless R6G through a Hg2+-promoted ring-opening process of R6G derivative. An extremely low detection limit for Hg2+ (6 × 10−9 M) can be achieved. These results demonstrate that fluorescent PMOs have great potential as supporting materials for enhanced fluorescence chemosensors.